This invention relates to mechanical power presses for stamping sheet material and the like and more particularly to the type of power press known in the art as a mechanical press wherein the frame of the press has a base portion for receiving sheet metal stamping or forming dies and the crown of the press has eccentric or crankshaft means for driving a vertically reciprocal slide toward and away from the bed of the press to effect pressing strokes. The slide is supported and guided for such reciprocation by the frame of the press.
In the prior art a number of patents show means for stopping operation of a mechanical punch press when the load exceeds a given limit to prevent undesired overload of the press. A common method of accomplishing this purpose is by interposing hydraulic fluid between the mechanical drive means and the reciprocating slide of the press, for instance as shown in Pels U.S. Pat. No. 1,808,606 and Stevens U.S. Pat. No. 2,438,951, and by providing means to shut down the press when a predetermined hydraulic pressure force is exceeded. In fact, this is the usual method of terminating press operation in mechanical presses when overload occurs.
In some of these prior patents the excess hydraulic pressure generated by the mechanical overload of the press is applied to a transducer which develops an electrical signal which terminates press operation.
It would be highly desirable to provide a press overload control of the type wherein excess hydraulic pressure generated by the mechanical overload of the press is utilized by the control and wherein the control can distinguish an actual press overload condition from a mere increase in hydraulic pressure caused by non-overload conditions, such as during setting of the hydraulic arrangement.